Objective:

The main objective of this research project
is to use Maxwell's equation for evaporation of an isolated drop to model
the evaporation of polydisperse multicomponent oil droplets at normal temperatures.

During machining, polydisperse mist droplets are generated from multicomponent
oils used as metalworking fluids. As these droplets travel with an airstream,
they are subject to evaporation. The resulting vapor will pass through mist
collectors and enter factory air, where it may recondense on particles or surfaces,
be inhaled by workers, or be emitted to the atmosphere. Within each droplet
size, relationships describing the change in mass with time for small droplets
(diameter < 20 mm) are numerically integrated over time for the most prevalent
compounds in the oil. Decreases or increases in mass for individual droplets
are linked by their combined influence on vapor concentrations. Experiments
conducted with mineral oil mist demonstrate that the model predicts evaporation
accurately. The model indicates that under some conditions, as much as 65 percent
of the mass in a mineral oil mist can volatilize within 10 seconds. The amount
of vaporization will depend on the initial concentration, size distribution,
and composition of the mist. Substitution of an alternative oil as a machining
fluid may decrease evaporation considerably.

Approach:

Industry uses metalworking fluids during the machining
of metal parts to cool, clean, and lubricate tools and workpieces. Petroleum-based
mineral
oils, mixtures of liquid organic compounds that boil over a broad range of
temperatures, are commonly utilized as metalworking fluids, either directly
as straight oils or as emulsions of oil in water called "soluble oils." As
the fluids are poured or sprayed liberally over the cutting zones, polydisperse
mist droplets may be generated by the rotational motion of flooded workpieces
and tools, the spray application of the oil, and condensation of hot vapor
from the cutting zone. Because most airborne droplets generated by machining
operations have diameters smaller than 10 mm, they may travel large distances
through factory buildings to deposit on distant surfaces or enter worker's
breathing zones.

More than one million workers are exposed to droplets generated by machining
operations. Oil mist droplets that are inhaled or contact skin can cause a
variety of health problems. Worker exposure to cutting fluids can result in
dermatitis and respiratory problems. Epidemiologic studies indicate that long-term
exposure to metalworking fluids can lead to increased incidence of several
types of cancer. The International Agency for Research on Cancer has concluded
that there is "sufficient evidence" that mineral oils used in the
workplace are carcinogenic.

To reduce amounts of metalworking fluid mist in factory air, hoods or enclosures
are installed to capture droplets near machining operations. Captured aerosol
is fed through ducts to mist collectors, which efficiently remove droplets
from the airstream before the cleaned air is recirculated.(15) As oil droplets
travel to collectors, they may experience partial or complete evaporation,
depending on the composition of the oil. Semivolatile organic compounds (SOCs)
that evaporate from the droplets will penetrate through the collectors and
return to the room air. These organic vapors may adversely affect worker health or serve as a source of fugitive.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.